Packaged arrangements of inductive coils are used extensively in telephone communications systems in which there is a need to add inductance to various types of circuits. In multi-pair conductor cable transmission systems, inductive coil assemblies are used to compensate for capacitance between conductor pairs. Assemblies of toroidally wound coils also find utility as inductive devices which are used to balance subscriber lines in telephone exchanges.
In order to load the conductors inductively, a cable is cut and coil assemblies are connected in series with the conductors to condition the electrical signals. Typically, groups of the coils, which are called loading coils, are placed a predetermined distance apart which may be on the order of about 1.6 kilometers.
The coils themselves are usually grouped together in an enclosure, which is referred to as a loading coil case. Generally, the loading coil case is a contoured plastic shell that includes a plurality of individual loading coil assemblies encapsulated in a potting compound such as polyurethane, for example, and that is either suspended from a cable or from a pole adjacent to the point at which the coil assemblies are spliced into the cable.
One problem associated with the manufacture of loading coil assemblies is that each of the individual toroidal coils in the load coil case includes two windings of relatively small size conductors such as, for example, 30 guage, the ends of which must be terminated and connected to conductors of the cable which is to be loaded. When coils wound of such size conductors are connected into electrical circuits, it is necessary to devise a means of connecting the coil conductors electrically to the relatively heavier conductors of a cable circuit without straining the coil conductors or breaking them. In many types of mounted transformers and coils, the ends of the windings are soldered to permanent terminals secured to insulating strips fastened to the coil mountings or to containers in which the coils are disposed.
Numerous prior art arrangements have been devised to package loading coils in an attempt to facilitate their assembly and the wiring of compact assemblages of individual coils. An example of the prior art may be found in U.S. Pat. No. 2,147,245 which discloses stacks of toroidal coils mounted on dowels and positioned within slit circular metallic tubes so that a number of tubes may be assembled and encapsulated within a metal casing. Further examples of packaged loading coils are disclosed in U.S. Pat. Nos. 2,548,199, 2,548,205, and 2,548,206, all of which issued on Apr. 10, 1951, in the names of E. J. Crane et al, W. M. Drobish et al, and E. L. Dron, respectively.
In order to provide a loading coil assembly which includes a compact array of individual toroidal coils that are relatively easy to connect within an inexpensive lightweight casing, a stack of coils are enclosed within a D-shaped case so that connection spaces for terminal strips are provided at the junctions of linear and arcuate sections of the case. This arrangement is disclosed and claimed in a copending commonly assigned application Ser. No. 864,304 filed Dec. 27, 1977 in the names of J. D. Eyestone and M. E. Szymanski, and now U.S. Pat. No. 4,172,965. The leads from the windings are wave-soldered to associated pins of the aforementioned terminal strips, after which plastic insulated conductors of a stub cable are connected to the pins and soldered so that the other ends of the stub cable may be connected to the cable, which effectively puts the loading coils into series with the outside plant cable to permit the coils to condition the transmission signals. These encased stacks of terminated coils, which are referred to as D-packs, may be compactly assembled into a molded outer casing such as that disclosed, for example, in copending, commonly assigned application Ser. No. 864,303 filed Dec. 27, 1977 in the name of J. Reinebach, and now U.S. Pat. No. 4,172,964.
While this arrangement replaces one in which a plurality of the load coils were arranged in layers, it does not provide a solution for the problem of the simple termination of relatively small gauge conductors of each individual coil, preferably by solderless techniques, prior to assembly into a stack. Moreover, it does not facilitate the individual testing of terminated inductive coils prior to their assembly into a D-pack, so that if a defective loading coil is found subsequent to its assembly into a D-pack, additional costs are incurred in its removal from the stack and replacement with an acceptable coil.
The prior art includes devices such as those shown, for example, in U.S. Pat. No. 3,979,615 for interconnecting substantially different gauge size conductors. While the arrangement in this last identified patent provides a contact element which simplifies the connection of a coil lead, for example, to a larger gauge size conductor, it is not adaptable to be assembled into a stack nor machine terminated. See also U.S. Pat. No. 4,038,573.
Seemingly, the known prior art does not include a solution for packaging and terminating individual coils in a manner which facilitates testing on an individual basis and which is adaptable to the mounting of a plurality of the coils in a stack for assembly into a case for use in outside telephone plant.